1. Field of the Invention
The present invention relates to methods for protecting cells and batteries which contain cells. The present invention also relates to protected cells and protected batteries which contain cells and methods for producing such a protected cell and battery.
2. Discussion of the Background
Batteries comprising lithium-based cells can provide the highest energy density of all rechargeable (secondary) cells. Cells are available in a range of energy densities, power densities and packaging options. This energetic battery technology comes at a price, however, as the cells are known for causing a fire hazard when misused.
Today's batteries may be constructed using lithium polymer pouch cells. These pouch cells are welded together to form what are sometimes referred to as bricks, assemblies, or quanta. The quanta are encapsulated and then they are arranged mechanically and electrically to create a battery pack.
Recently, fires caused by lithium-based battery packs have called into question the intrinsic safety and safety testing of such batteries. Currently, there is no alternative for battery power that has high energy density, long cycle life and is safe.
Through good electronics and packaging design, the chance of fires in lithium battery packs can be reduced to a reasonable level. However, even in the best design, fires within cells can and do occur. In many cases a fire in a single cell may be tolerable, but a fire in a multiple cell pack caused by a single cell can quickly turn in to a high energy conflagration that is difficult to extinguish.
Primary batteries (single-use) and secondary batteries (rechargeable) are subject to internal or external failures that cause conflagration of the cell. This conflagration has been shown to propagate rapidly from cell to cell and from battery to battery, releasing tremendous amounts of thermal energy risking human life, facilities, and vehicle platforms.
Thus, there remains a need for lithium-based cells and batteries that are substantially free from the above-discussed problems. In particular, there remains a need for a safe battery system with high power density and high energy and which eliminates or significantly reduces the chance of and extends the time to failure of a cell or battery.